Recently, demand for highly developed data processing has become greater as the amount of data to be processed in a photographic camera increases. To meet such demand, information on accessories such as interchangeable objectives (lens assemblies) must be transmitted to an operational circuit in the camera body. In the case of an interchangeable objective, for example, typical information is the fully opened diaphragm value, the fully stopped down diaphragm value, and a preset diaphragm value in the manual mode. In a camera system with which an interchangeable objective including an auto-focus mechanism can be used, additional information such as a signal representing the shortest distance for focussing and a focussing detection signal must also be transmitted to the operational circuit. To meet such demand, U.S. Pat. No. 4,357,089 discloses oppositely paired electrical contacts on the camera mount and the lens mount, which exhibit compactness, maneuverability and other features required for a data transmission mechanism. The disclosure of this patent is incorporated fully herein by reference.
When the data transmission is carried out by these pairs of respectively opposed electrical contacts, each pair is usually constructed for reliable electrical contact so that the one electrical is spring-biased to project through the face of the associated mount, whereas the other electrical contact is flush with or recessed slightly from the face of the associated mount. These pairs of respectively opposed electrical contacts usually include one or more pairs for transmission of information peculiar to said interchangeable objective or the like and a single pair serving to indicate the operational mode of the photographic camera. The last-mentioned pair of electrical contacts is described in the referenced patent as the pair of electrical contacts for changeover between an AUTO photographing mode in which the diaphragm value is automatically controlled and a MANUAL photographing mode in which the diaphragm value is manually set. The changeover contacts may be replaced by a pair of electrical contacts functioning to indicate changeover between a photographing mode in which the diaphragm value or the shutter speed or both can be automatically adjusted and a conventional mechanical photographing mode in which the diaphragm value is adjusted and the shutter is actuated, both in a mechanical manner, to achieve reliable photographing even after the battery source has been consumed to some degree.
Thus, the pairs of respectively opposed electrical contacts include one or more pairs of electrical contacts exclusively for transmission of the information peculiar to the interchangeable objectives or the like and generally a single pair of electrical contacts for mode control, i.e., for transmission of a signal indicative of the operational mode selection. Concerning the last-mentioned pair of electrical contacts for selection of the operational mode, the stationary electrical contact must always be recessed from the face of the associated mount to avoid interference of this contact with the other pairs of electrical contacts as the objective is secured to the camera body. The spring-biased electrical contacts of the pairs of electrical contacts for transmission of information peculiar to the objective are installed in the same mount as the stationary electrical contact of the pair of electrical contacts for mode control, in order to avoid interference of the former contacts with the latter.
To achieve the necessary data transmission through these pairs of respectively opposed electrical contacts, it is essential that each pair of opposed electrical contacts be reliably brought into mutual physical and electrical contact. However, foreign substances produced due to environmental conditions, particularly fragments of insulator, often cling to or accumulate on the effective surfaces of each pair of opposed electrical contacts or in recesses defined by these electrical contacts and thereby adversely affect the electrical conduction between each pair of electrical contacts, resulting in unreliable transmission of information.
Accordingly, it is important to remove any foreign substances deposited on the electrical contacts. However, it is not practical to force the user to remove such foreign substances every time the user mounts an interchangeable objective on the camera body. Further, when foreign substances accumulate in the recesses defined by the electrical contacts in the mount, a suitable cleaning implement for removing such foreign substances would likely be necessary, since the electrical contacts are so small in size, but providing such a cleaning implement is not practical.